PDE4A and asthma: Nunes et al. [53] reported the optimization of the sulfonamide prototype LASSBio-448 (63) [54], a PDE4 inhibitor (PDE4A IC50 = 0.7 μM; PDE4D IC50 = 4.7 μM), for the treatment of pulmonary inflammatory diseases such as asthma (Figure 17.